In the late 1980s powder injection molding processes including metal injection molding (MIM) and ceramic injection molding (CIM) were established. In these processes finely-powdered metal or ceramic material is mixed with a measured amount of binder material to form a ‘feedstock’ capable of being handled by plastic processing equipment through a process known as injection mold forming. The molding process allows complex parts to be shaped in a single operation and in high volume. The final products of such processes are commonly component items used in various industries and applications.
In these processes the molding step involves the use of injection molding machines and results in the formation of a so-called green body. This green body undergoes a further step in which the binder is typically at least partially removed before the body is heated to temperatures where the metal or ceramic components are sintered.
A feedstock is required also for more modern processes for forming prototypes such as 3D printers. In some aspects however the feedstock for 3D printing devices has been found to require different properties as will be explained below.
Creating a feedstock for 3D printing devices is not an easy feat as there are multiple parameters that should be adjusted. The final feedstock product must in particular meet the flexibility, stiffness, stickiness and viscosity required for successful 3D printing.
In the field of 3D printing the fused deposition modelling (FDM) process is increasingly being used for manufacturing consumer goods, warranting an improvement in the quality of the 3D printed object output.
Fused deposition modelling is an additive manufacturing technology commonly used for modelling, prototyping, and production applications. FDM is a rapid prototyping technique and it is one of mechanical manufacturing technologies, in which the process of extrusion of feedstock materials is involved. Generally, FDM works by laying down material in layers.
It is known that volumetric flow errors compromise the quality of the printed product. The thermoplastic filament itself has a significant effect on the variability in an FDM extruder's flow. In other words, depending on its material the feedstock filament contributes to volumetric flow errors.
Furthermore, without wanting to be bound by theory it is believed that in terms of mechanical design, the size and tolerance of the filament diameter is found to play a very significant role in determining flow characteristics of the extruder.
Ideally, the diameter of the filament used can be minimized and a filament can be manufactured with tighter diameter tolerances to reduce volumetric flow errors.
Also, in the development of new feedstock composite materials need to be selected with reasonably good mechanical and thermal properties as well as their capabilities of mixing and surface bonding with binders.
In view of the above, there is a need for new feedstock for 3D printing devices which can be formed into a filament of constant diameter and which also meets the further material requirements such as sufficient hardness, suitable viscosity, good extrusion properties as well as a good adhesion of the printed mass strands to each other.
The stickiness is at least one property by which a feedstock suitable for 3D printing devices differs from a feedstock that is commonly used in powder injection molding (PIM) or powder extrusion molding (PEM) processes. A feedstock suitable for 3D printing requires good bonding ability of the individual mass strands between each other in order to produce a 3D structure with high resolution and good reproducibility. This property of the feedstock is however not beneficial with powder injection molding (PIM) or powder extrusion molding (PEM), in particular if these applications involve a smoothing calendar, a slit die or similar means. In fact, in PIM or PEM applications such stickiness is rather undesirable, and is generally avoided by preparing a specific feedstock that does not have this property, for example by including anti-adhesion additives.
It was an object of the invention to provide a novel feedstock material suitable for 3D printing devices meeting the above outlined criteria.